Isoprenoidal alcohols

Porphyrins and Plant Pigments Chiorophyii Hemin Carotenes and Xanthophyiis > Chlorin Phaeophytin hydrocarbons Phytane, pristane, carotenoids, isoprenoids, alcohols, ketones, acids, porphyrins... 

One of the most impressive findings has been the discovery of lipid intermediates in the biosynthesis of polysaccharides (see Refs. 2 and 465.) At least two structurally different types of these compounds exist the intermediate may be an isoprenoid alcohol ester of the glycosyl pyrophosphate or the analogous derivative of the glycosyl phosphate. Derivatives of the first type are formed by reaction between the sugar nucleotide and the alcohol phosphate, for example, undecaprenyl phosphate (120), which participates in the biosynthesis of Salmonella lipopolysaccharide.466... 

In the first Section, the dolichol pathway of protein glycosylation is introduced, and the reader is made familiar with the various reactions in the formation of the lipid and carbohydrate moieties of lipid-linked saccharides. Three different classes of compound are known so far (a) isoprenoid alcohol esters of monosaccharide monophosphates, such as D-mannosyl and D-glucosyl (dolichol phosphate), (b) such isoprenoid alcohol esters of saccharide diphosphates as dolichol diphosphate linked to 2-acetamido-2-deoxy-D-glucose and to oligosaccharides, and (c) retinol (D-mannosyl phosphate). The dolichol-linked sugars occur in all eukaryotes. 

Many of the proteins of membranes are enzymes. For example, the entire electron transport system of mitochondria (Chapter 18) is embedded in membranes and a number of highly lipid-soluble enzymes have been isolated. Examples are phosphatidylseiine decarboxylase, which converts phosphatidylserine to phosphatidylethanolamine in biosynthesis of the latter, and isoprenoid alcohol phosphokinase, which participates in bacterial cell wall synthesis (Chapter 20). A number of ectoenzymes are present predominantly on the outsides of cell membranes.329 Enzymes such as phospholipases (Chapter 12), which are present on membrane surfaces, often are relatively inactive when removed from the lipid environment but are active in the presence of phospholipid bilay-ers.330 33 The distribution of lipid chain lengths as well as the cholesterol content of the membrane can affect enzymatic activities.332... 

Isoprenoid alcohol phosphokinase 409 Isoprenoid compounds. See also Polyprenyl compounds... 

Other groups that can be attached covalently to enzymes include fatty acids, isoprenoid alcohols such as far-nesol, and carbohydrates. Although such modifications are widespread, our understanding of how cells use them to regulate enzymatic activities is still fragmentary. 

Vitamin A (trans-retinol) is called an isoprenoid alcohol because it consists, in part, of units of a single five-carbon compound called isoprene ... 

The propionyl side chain of ring IV is esterified with a long-chain isoprenoid alcohol. 

The identification of an isoprenoid alcohol kinase in Klebsiella aerogenes and Escherichia coli382 supports the view that enzymic phosphorylation and dephosphorylation of C55 isoprenols is the basis of a control mechanism of polysaccharide synthesis by bacterial membranes. 

Methanogen lipids have been intensively studied and characterized due to their structures being one of the most remarkable features that distinguish the Archaea from all other organisms (Woese et al., 1990). The polar lipids of methanogens comprise both di- and tetra-ethers of glycerol and isoprenoid alcohols with most compounds being based on the core lipids archaeol (12) or caldarchaeol (13). Minor core lipids are sn-2- and i -3-hydroxyarchaeol and macrocyclic... 

C-racemization of phosphorothioylated/phosphorylated amino acids (Scheme 23). An oxathiaphospholane approach to one-pot phosphorothioylation of isoprenoid alcohols such as allyl, geranyl, isopentenyl, citronellyl, farnesyl, and phytyl alcohols has also been reported (Scheme 24). ... 

First, we will take up cyclopropyl group formation by the rearrangement of carbon skeletons via cationic intermediates encountered in various mono- and sesquiterpenes, and also examine the illudin biosynthesis where contraction of a cyclobutyl cation to a cyclopropane has been invoked. We will then discuss the head-to-head condensation of isoprenoid alcohols at the C15 or C20 level to generate the cyclopropyl intermediates, presqualene pyrophosphate and prephytoene pyrophosphate, on the way to the C30 and C40 polyene hydrocarbons, squalene and phytoene respectively. Conversion of 2,3-oxidosqualene via common intermediate protosterol cation to cycloartenol or lanosterol represents an important pathway in which the angular methyl group participates in the three-membered ring formation. The cyclopropanation outcome of this process has been carefully studied. 

The propionyl group on ring IV of Chls a and b and BChl b is esterified by the long-chain isoprenoid alcohol phytol. In BChl a the propionyl group is esterified by either phytol or the all-fran geranylgeraniol, depending on the bacterial species [see Fig. 5 (B)]. 

The three-carbon core of such molecules most often consists of glycerol, with the hydrophobic tails being made of long-chain fatty acids hnked to glycerol by ester bonds - except in archaebacteria, where they are formed by isoprenoid alcohols hnked to glycerol (in the chiral configuration opposite to that shown in Scheme... 

Vitamin A - also called all-tra/75 -retinol, is an isoprenoid alcohol that plays a key role in vision and a role in controlling animal growth. Vitamin A must either be present in the diet, or derived from / -carotene, an isoprenoid compound prominent in carrots. See Figure 19.25 for the biosynthesis of dX -trans-xQtmo. Dehydrogenation of retinol yields the aldehyde, retinal, which has a role in vision. Another derivative of retinol is retinoic acid, which can be made by the oxidation of retinal. 

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